This application is a 35 USC 371 application of PCT/DE 00/02028 filed on Jun. 21, 2000.
1. Field of the Invention
The invention relates to a common rail injector for injecting fuel in a common rail injection system of an internal combustion engine, in particular a large diesel engine, having an injector housing which communicates with a central high-pressure reservoir and in which a nozzle needle can move axially counter to the initial stress of a nozzle spring which is contained in a nozzle spring chamber, in order to adjust the injection onset and the injection quantity as a function of the position of a 3/2-way valve.
2. Description of the Prior Art
In known common rail injection systems, a high-pressure pump feeds the fuel into the central pressure reservoir, which is referred to as the common rail. High-pressure lines lead from the high-pressure reservoir to the individual injectors, which are associated with the cylinders of the engine. The injectors are individually triggered by the engine electronics. The rail pressure prevails at a pressure-balanced 3/2-way solenoid valve which keeps the high-pressure bores to the conventional injector free of pressure. Only when the magnet is supplied with current does the 3/2-way solenoid valve open the connection from the rail to the injector and the fuel travels into the combustion chamber via the nozzle needle, which has lifted up counter to the spring force. The injection onset and the end of injection are thus determined by the beginning and end of the power supply to the magnet. The duration of the power supply is decisive for the injection quantity.
Pressure waves occur during operation of the injection system and are damped in the central high-pressure reservoir. In order to achieve a favorable damping action, the volume of the central high-pressure reservoir must be of sufficient size. An increasing volume of the central high-pressure reservoir, however, has a negative influence on the starting behavior and the dynamic behavior of the injection system because the time required for changing the system pressure increases.
The object of the present invention is to improve the damping behavior in a common rail injection system.
In a common rail injector for injecting fuel in a common rail injection system of an internal combustion engine, in particular a large diesel engine, having an injector housing which communicates with a central high-pressure reservoir and in which a nozzle needle can move axially counter to the initial stress of a nozzle spring which is contained in a nozzle spring chamber, in order to adjust the injection onset and the injection quantity as a function of the position of a 3/2-way valve, the object is attained by virtue of the fact that an injector pressure reservoir is integrated into the injector housing and communicates with the central high-pressure reservoir independent of the position of the 3/2-way valve. The pressure reservoir is used to damp the pressure waves coming from the central pressure reservoir during and after the injection.
One particular embodiment of the invention is characterized in that the volume of the injector pressure reservoir is 10 to 20 times the maximal injection quantity.
This value has turned out to be particularly advantageous in experiments carried out within the scope of the current invention.
Another particular embodiment of the invention is characterized in that the injector pressure reservoir communicates with a pressure-free chamber by means of a damping unit integrated into the injector housing. The total volume of the injector pressure reservoir and the central high-pressure reservoir can be considerably reduced as a result of the damping achieved by the damping unit.
Another particular embodiment of the invention is characterized in that the damping unit includes a damping throttle and a safety valve. Normally, the central high-pressure reservoir is equipped with a safety valve which opens in the event of an overpressure. This can be the case, for example, if the system pressure control circuit is not functioning properly. In the event of a possible mechanical failure of the safety valve controlled by the system pressure control circuit, serious damage to the engine can occur. Integrating the safety valve into the injector housing increases system safety. In addition, the safety valve normally provided in the central high-pressure reservoir can be eliminated.
Another particular embodiment of the invention is characterized in that the damping throttle is integrated into a screw plug which is screwed into the injector housing between the nozzle spring chamber and the injector pressure reservoir. This embodiment has the advantage that it can be produced in a particularly simple and inexpensive manner.
Another particular embodiment of the invention is characterized in that the injector pressure reservoir communicates with a fuel tank via the damping unit integrated into the injector housing. This offers the advantage that the injector pressure reservoir is discharged into the fuel tank if the pressure in the injector reservoir is greater than the system pressure.